With recent widespread use of computers, inkjet printers have come to be used not only at offices but also at home for printing images on paper, film or cloth.
Inkjet recording methods include a method of applying pressure by a piezo element, thereby discharging ink droplets, a method of generating air bubbles in an ink by heat, thereby discharging ink droplets, a method using ultrasonic waves, and a method of sucking and discharging ink droplets by making use of electrostatic force. As inks for such inkjet recording, aqueous inks, oil-based inks and solid (fusible type) inks are used. Of these, an aqueous ink is most popularly used in consideration of manufacturing ease, handling ease, odorlessness and safety.
A colorant to be incorporated in such inkjet recording inks is required to have high solubility in a solvent, permit high-density recording, have a good color hue, have excellent fastness to light, heat, air, water or chemicals, have good fixability to an ink absorbing material without bleeding, have excellent storage stability as an ink, be free from toxicity, have a high purity and be available at a low cost. Above all, as the electrical data capacitance of digital image becomes higher, there is an increase need for more precise and higher-quality image recording. To meet this need, it is necessary to form finer ink droplets and prevent spreading of ink droplets which have landed on a recording layer. Bleeding of a dye caused by spreading of ink droplets cannot be inhibited completely by an improvement in the recording layer. There is accordingly a strong demand for means capable of preventing bleeding of a dye contained in the ink solution by improving an ink or drawing method.
As means for preventing bleeding of a dye by improving an ink solution, various methods were tried including increase in the viscosity of the ink solution, use of a low diffusible and coarsened coloring material and incorporation of a mordant. By these methods, however, it is not impossible to prevent bleeding of an image and keep time-dependent stability of the ink solution or prevent clogging of a drawing nozzle at the same time.
Upon recording of a multicolor image, multicolor and/or multi-gradation image signals are output using an ink set having a series of inks different in color hue or density, or different in both of them. This case is however accompanied with such a drawback that when one of the inks tends to cause bleeding, it induces bleeding of another bleeding-free ink which is used in combination therewith. Compared with prevention of bleeding of an ink to be used alone, prevention of bleeding of an image recorded by an ink set is complicated and difficult so that no satisfactory solution has been found yet.